<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
  .box {
    width: 200px;
    height: 200px;
    background-color: green;
    /* display: none; */
    opacity: 0;  /*transition 过度效果 */
    /* overflow: hidden; */
    visibility : hidden;
    /* position: absolute;
    left: -9999px; */
    /* transform: scale(0); */
  }
  .box:hover{
    opacity: 1;
    transition: opacity 5s;
  }
  /* .container {
    height: 0;
    overflow: hidden;
  } */
  </style>
  
</head>
<body>
  <!-- <div class="container"> -->
    <div class="box"></div>
    ddddd
  <!-- </div> -->
</body>
</html>
